For the purpose of cleaning the surface of precision parts, machine tools and the like by removing stains consisting mainly of organic substances such as fat and oil, machine oil, cutting oil, grease, crystalline liquid, flux and the like, various cleaning agents have been used. For example, hydrocarbon solvents such as kerosin, benzene, xylene and the like; chlorine-based solvents such as trichloroethylene, tetrachloroethylene and the like; flon-based solvents such as trichlorotrifluoroethane and the like; and aqueous cleaning agents blended with surface active agents, builders and the like have been conventionally used. Especially, for cleaning electronic, electric and machine parts, flon- or chlorine-based solvents have been used, taking advantage of their characteristic properties of high detergency and incombustibility.
However, cleaning agents which comprise flon- or chlorine-based solvents have serious problems in terms of safety, toxicity, environmental pollution and the like. On the other hand, hydrocarbon solvents, especially benzene, xylene and the like, have high toxicity and are characterized as toxic substances according to industrial safety and hygiene standards. Consequently, use of such hydrocarbon solvents as cleaning agents is not preferable when hazardous and complex handling of these substances is taken into consideration.
Aqueous cleaning agents are not so hazardous and have a low toxicity in comparison with cleaning agents containing solvents, and their detergency can be improved by optionally selecting cleaning agent composed of elements such as surface active agents, builders and the like. However, being highly soluble in water in general, these aqueous cleaning agents have the disadvantage of markedly poor processability of the rinsing waste water which is discharged when a cleaning liquid adhered to a material to be washed is rinsed with an aqueous rinsing solution. Although treatment of such rinsing waste water can be carried out making use of coagulating sedimentation, pressure floatation, activated sludge methods, active carbon treatment or the like, each of these treatment processes is expensive and requires additional equipment.
Consequently, great concern has been directed toward the development of an industrially advantageous process for cleaning of electronic parts, precision parts or the like, which does not require such expensive waste water treatments or additional equipment therefor.